In recent years, a laser device which employs a laser element such as a semiconductor laser (LD; Laser Diode) element has been commercialized and is spreading in the field of optical communications. Examples of the laser device include a laser module obtained by combining a laser element and an optical fiber. For such a laser module, it is necessary to combine the laser element and the optical fiber so that optical coupling is achieved with a high optical coupling rate.
As such, in the laser module, it is important to align precisely (i) an output surface (surface via which laser light is outputted) of the laser element and (ii) a leading end portion of the optical fiber so that more of the laser light emitted from the laser element is introduced to the optical fiber. It is also important to keep the output surface of the laser element and the leading end portion of the optical fiber in alignment with each other.
As the laser module as described above, for example, a laser module described Patent Literature 1 has been known. In the laser module described in Patent Literature 1, a laser element (laser) and an optical fiber are provided on the same substrate. Specifically, the laser element is attached onto a laser submount which is fixed onto the substrate. Similarly, the optical fiber is attached onto a fiber submount (fiber supporting member) which is fixed onto the substrate.
In the laser module described in Patent Literature 1, the laser element and the optical fiber are attached by means of soldering onto the laser submount and the fiber submount, respectively, in a state where the laser element and the optical fiber are aligned with each other. This allows an output surface of the laser element and an leading end portion of the optical fiber to be in alignment with each other.
When the optical fiber is attached to the fiber submount by means of soldering as described above, it is necessary to not only increase a temperature of solder to a melting point or higher, but also sufficiently increase a temperature of the fiber submount, particularly a temperature of a solder fixation section to which the solder is applied so as to be spread. This is because the solder applied to the solder fixation section cannot be spread uniformly over the entire solder fixation section, in a case where the temperature of the solder fixation section is low.
In general, laser light outputted from a laser element spreads so that (i) a full width at half maximum (FWHM) of an angle of divergence in a longitudinal direction (direction perpendicular to an active layer of the laser element) of an output surface of the laser element is about 40° and (ii) a full width at half maximum of an angle of divergence in a lateral direction (direction parallel to the active layer of the laser element) of the output surface is about 10° (see, for example, Nonpatent Literatures 1 and 2). That is, the laser light spreads wider in the longitudinal direction than in the lateral direction.
As such, a technique as described in Nonpatent Literatures 1 and 2 has been generally practiced in which technique a leading end portion of an optical fiber is formed to have a wedge shape and is given a lens function, so that laser light which spreads widely in a longitudinal direction efficiently enters a core section of the optical fiber.
This makes it possible to prevent (i) undesirable application of laser light to around solder for attaching the optical fiber to the fiber submount, which laser light has been outputted from the laser element toward the core section of the optical fiber or (ii) undesirable introduction of the laser light to the clad section of the optical fiber, which laser light has been outputted from the laser element toward the core section of the optical fiber.